1. Field of the Invention
The invention relates to a vehicle driver advisory controller for guiding a driver in developing a driving behavior to obtain optimum overall vehicle fuel economy without significantly compromising vehicle powertrain performance.
2. Background Discussion
Hybrid electric vehicle powertrains having both an electric power source and a mechanical power source provide improved engine fuel efficiency and reduced undesirable exhaust gas emissions in comparison to a conventional vehicle powertrain. One example of a hybrid electric vehicle powertrain is described in U.S. Pat. Nos. 6,907,325; 6,994,360; and 7,013,213, which are assigned to the assignee of the present invention.
The hybrid electric vehicle powertrain disclosed in these patents, sometimes referred to as a full-hybrid powertrain, has a power-split power flow path from each power source to vehicle traction wheels. The power developed by the electric power source is integrated with power developed by the mechanical power source using a planetary gearset with separate elements of the gearset being drivably connected to an internal combustion engine, a generator and a motor. A vehicle control system is designed to optimize fuel economy, reduce undesirable engine exhaust gas emissions and manage power delivered to traction wheels without compromising vehicle performance. The powertrain emulates electronically the performance characteristics of well-known continuously variable vehicle transmissions.
The powertrain has a potential for improving fuel economy by enabling the engine to operate in its most efficient region independently of vehicle speed. The achievement of high fuel economy, however, depends to a large extent upon driver behavior, which plays a significant role in full utilization of the advantages of a hybrid electric vehicle powertrain.
Although a power-split hybrid powertrain will be disclosed, various other hybrid electric vehicle powertrain configurations and control technologies could be used in practicing the strategy of the present invention. The best results are achieved by shaping and limiting the driver demand for power to improve overall fuel economy under normal driving conditions without reducing the vehicle's performance under both heavy load conditions and heavy acceleration driver demand.
Hybrid electric vehicles usually are classified into three types; i.e., series hybrid systems, parallel hybrid systems, and power-split hybrid systems. A power-split hybrid system, which is capable of incorporating the present invention, provides characteristics of both a series system and a parallel system. A power-split hybrid system uses a planetary gearset to connect an internal combustion engine, a generator and a motor, although other engines, such as a fuel cell power plant also could be used.
A power-split hybrid electric vehicle powertrain provides the driver with an ability to use an electric drive mode using a traction motor, wherein traction power is applied using power of a high voltage battery only. It also can operate in a hybrid drive mode using reaction torque of the generator to control engine speed as traction power is delivered to the wheels from both the engine and the motor. In this mode of operation, the engine is operated at its most efficient region independently of vehicle speed. A high voltage battery acts either as an energy storage medium, or as an additional power source for the motor. The generator and the motor, together with the engine in a power-split hybrid electric vehicle, require a highly coordinated vehicle control system with control algorithms residing in a vehicle controller to perform a blending of torque, speed and power of the two power sources.